1. Field Of The Invention
The present invention relates to glycol antifreeze mixtures and more particularly to glycol antifreeze mixtures containing an improved defoaming agent.
2. Description Of The Prior Art
Glycol-based antifreeze formulations containing corrosion inhibitors such as borates, silicates, phosphates, caustic, mercaptobenzothiazole, tolyltriazole, nitrates, nitrites and other inhibitors listed in the patent literature do not, by themselves, exhibit excessive foaming tendencies. However, when these glycol-based antifreezes containing the above-mentioned inhibitors are diluted with water for use in internal combustion engine cooling systems, excessive foaming occurs. This foaming causes a loss of coolant from the system and possible subsequent damage to the engine.
It is common practice to include in the glycol-based antifreeze formulations an agent or combination of agents to reduce the foaming of the water-diluted base antifreeze solution. The most commonly used defoaming agents are silicones and polymers of ethylene oxide or propylene oxide or ethylene oxide and propylene oxide copolymers commonly referred to as polyols. The latter type of defoaming agent has been used extensively, and certain modifications thereof have also been used. For example, U.S. Pat. No. 2,923,686 teaches the adduct of propylene oxide and ethylene oxide on glycerol, with each hydroxyl group of the glycerol nucleus being provided with an adduct. These compounds generally have a very low water solubility, but the solubility is sufficient to form a unitary phase in the very low concentrations used.
Certain desirable corrosion inhibitor systems are particularly likely to increase the foaming problem when placed in automobile cooling systems. For example, an excellent corrosion inhibitor is disclosed and claimed in U.S. Pat. No. 3,931,029. In this patent, a polymer is ethylene oxide and propylene oxide is suggested as a defoaming agent.
Antifreeze normally is formulated with 0.03 to 0.05% of defoaming agent. This concentration is necessary to maintain adequate defoaming action for the life of the permanent type antifreeze. A defoaming agent such as the polyol of U.S. Pat. No. 3,931,029 are normally used in the above concentration range. If added to the radiator within a relatively short period of time after it has been formulated, no problem exists, but frequently large scale users, such as the large automobile companies, store the antifreeze in large tanks that contain many thousands of gallons. Upon standing for several days to several months, the defoaming agent rises, forming an upper liquid layer. As a result, when antifreeze is drawn from the base of the tank it is deficient in defoamer and, if the tank is emptied completely, the last portion will be only defoamer, which is completely unsatisfactory as an antifreeze stock. This has been a very serious problem to antifreeze consumers as well as to antifreeze producers.